A scanner-control device of this type has applications in many technical areas, for example in a nonhomogeneous medium or on boundary surfaces, to receive reflected echo signals from transmit pulses and to evaluate them. Through an echo-time (e.g., delay time) measurement, information can be derived regarding, for example, the length of the distance that the signal has traveled. Examples of applications include distance measuring using sound, radar, or light waves. Furthermore, the echo signal shape can give information about the structure of the carrying medium, such as in determining the fog density in the atmosphere using light waves, or in seismic measurements of plate motion in the earth, or in measurements of material layers in pipes and walls using radar, to name only a few examples.
In most cases, an evaluation in real time, i.e., at the speed at which the echo signals arrive, is impossible due to the insufficient speed of the evaluation circuit. This is particularly true of the evaluation of signals that expand at the speed of light. Therefore, for this purpose, scanning devices are used in which the echo signal is scanned in a step-by-step manner, resulting in the desired time extension for the evaluation. In a scanning system of this type, a clock generator periodically triggers a pulse shaper, which sends transmit pulses to the system to be investigated. The returning echo signal is scanned in a scanner after a variable time .DELTA.T. The scanning value associated with a time point, after delay .DELTA.T, receives further signal processing. By varying delay .DELTA.T, the entire echo signal can gradually be reconstructed.
The conventional methods for generating scanning pulses delayed by a delay .DELTA.T are either imprecise or very expensive, particularly for very small increments and/or great variation ranges.
In U.S. Pat. No. 5,543,799, a local-range radar is described in which a variable, voltage-controlled delay of the transmit pulse takes place. The delay in certain circumstances is not a linear function of a control voltage and is therefore imprecise.
The Analog Devices Company offers a digital circuit arrangement having a controllable time delay (AD9501, AD9505), the linearity being maintained through generating a highly precise frame function.